you do have the option of paying normal prices though, but I'm not sure about the COP; what happens when you get to the half and full points of the COP bar? does the zone still increase for all of your CO units?

Presumably yes, and if that's the case you can pop out a CO infantry to save your bar if your other CO units are about to get downed. Seems a bit too good considering the CO(s) gets the COP more easily than everyone else except maybe 3 zoners

if no, then you end up with the aforementioned weaker Kanbei deal, although you could tamper with the cost of putting a CO in a unit, but then it really is just Kanbei.